Autogenous veins or arteries are the most common and most preferred conduits in revascularization of coronary and peripheral occlusive vascular disease. With the increasing age of the population and the increasing number of redo operations due to the development of intimal hyperplasia (an increase in the size of a tissue or organ due to an increase in the number of component cells) and accelerated atherosclerosis (obstruction of the arteries by localized fatty deposits) in bypass grafts, it is expected that over one third of patients will not have one or both of these conduits available at the time of revascularization. Prosthetic materials can be used for large diameter vessels; however their patency (state of being open or unblocked) is poor when used as conduits to replace small diameter vessels. There is, therefore, a need for alternative conduits, particularly for smaller diameter vessels. Cryopreserved arterial and venous allografts have been suggested as a possible "off-the-shelf" solution for small diameter vessel bypass. Clinical studies of these gmfts have been limited in both coronary and peripheral circulation, but demonstrate the significant stigma of poor patency irrespective of position.
Blood vessels are also a ubiquitous component of human vascularized tissues and organs, which may, one day, be successfully stored by cryopreservation for transplantation. Furthermore, providing that significant immunological issues can be overcome, cryopreserved xenografts may, one day, provide an unlimited supply of vascularized tissues and organs for storage by cryopreservation.
Although not commonly employed, polyethylene glycol (PEG) has been reported to be a cryopreservation agent (see "Pharmcological Considerations in Cryopreservation" by Shlafer in Organ Preservation for Transplantation, Karow AM and Pegg DE (eds) Marcel Dekker, New York, pp 177-212 (1981)). It has also been suggested that PEG may reduce the immune response to allogeneic blood transfusions and transplants (see "Molecular Camouflage of Antigenic Determinants on Intact Mammalian Cells: Possible Applications to Transfusion Medicine" by Murad et al. in Blood 88 (Supplement 1): 1765 (1996); "The Other Blood Substitute: Antigenically Inert Erythrocytes" by Scott et al.; and "Heart Preservation Solution Containing Polyethylene Glycol: An Immunosuppressive Effect" by Collins et al. in Lancet, 338:390 (1991)). A 30% reduction has been observed in the incidence of acute rejection in a group of heart transplant recipients in which the donor organ had been stored at 4.degree. C. in a solution containing 5%. In a subsequent study, PEG produced a modest but statistically significant increase in rat liver allograft survival time from 9.6 to 11.9 days (see "The Immunosuppressive Effect of Polyethylene Glycol in a Flush Solution for Rat Liver Transplantation" by Tokunaga et al. in Transplantation 54:756-8 (1992)). In these studies, the transplanted organ was merely soaked in the PEG solution without subsequent cryopreservation.
U.S. Pat. No. 4,938,961 to Collins et al. discloses an organ preservation solution containing polyethylene glycol, along with a variety of further ingredients including: 30-40mM NaOH, 100 mM Lactobionic acid, 25 mM KH2PO4, 10 mM KOH, 30 mM raffinose, and 3 mM glutathione. This solution is used for the transport of an organ from a donor to a recipient in cold solution.
In recent unpublished studies, it was found that the development of intimal hyperplasia in cryopreserved allografts is accelerated compared to fresh allografts due to the additional cryopreservation insults superimposed on the melee of other variables associated with the placement of veins into the arterial circulation.
Cryopreserved allografts have been shown to have extensive medial fibrosis, intnnal hyperplasia and a significant infiltrate consisting of activated macrophages, lymphocytes, granulocytes and plasma cells (see "Transplantation of Cryopreserved Canine Venous Allografts" by Bank et al. in J Surg Res 50:57-64 (1991), "Cryopreserved Venous Homografts as Vascular Conduits in Canine Carotid Arteries" by Showalter et al. in Surgery 106:652-659 (1989), "Evaluation of Cryopreserved Allograft Venous Conduits in Dogs" by Deaton et al. in J Thorac Cardiovasc Surg 103:153-162 (1992) and "A study of the Functional and Histological Differences in Autologous and Allogenic Vein Grafts-Two Different Vasculopathies" by Davies et al. in J Surg Res 69:14-22 (1997)).